Multiple pressure responsive control device for a variable area nozzle of a jet engine



R. J. COAR Aug. 16, 1955 2,715,311 MULTIPLE PRESSURE RESPONSIVE CONTROL DEVICE FOR A A VARIABLE AREA NOZZLE OF A JET ENGINE 4 Sheets-Sheet l Filed NOV. 18, 1950 O NTL Www EN QN MEL Allg. 16, 1955 R 1 CQAR 2,715,311

MULTIPLE PRESSURE RESPONSIVE CONTROL DEVICE FOR A VARIABLE AREA NOZZLE OF A JET ENGINE Filed Nov. 18, 1950 4 Sheets-Sheet 2 l: IG. 2

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AFTERBURNER OFF AND NOZZLE OPEN AFTERBURNER ON AND NOZZLE CLOSED P6 AFTERBURNER ON WITH NOZZLE OPEN OR p2 HRWWITH NOZZLE CLOSED INVENTOR R ICHARD J. @OAR AGENT Aug. 16, 1955 R. J. coAR 2,715,311

MULTIPLE PRESSURE RESPONSIVE CONTROL DEVICE FOR A VARIABLE AREA NOZZLE OF' A JET ENGINE Filed Nov. 18, 1950 4 Sheets-Sheet 5 vI- ICEL- FIGL INVENTOR R ICI-IARD J. COAFZ BY M/{mfn @mai AGENT Aug. 16, 1955 R. J. coAR 2,715,311

MULTIPLE PRESSURE RESPONSIVE CONTROL DEVICE FOR A VARIABLE AREA NOZZLE OF A JET ENGINE Filed Nov. 18, 1950 4 Sheets-Sheet 4 ZZZ RICHARD J. @OAR ENUM 7W,

AGENT United States atent Ofic MULTIPLE PRESSURE RESPONSIVE CONTRGL DEVICE FR A V AMABLE AREA NZZLE F A EET ENGIIIE Richard J. Coar, Hartford, Conn., assigner to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application November 18, 195i?, Serial No. 196,424

i4 Claims. (Cl. 6ft-35.6)

This invention relates to a control for a propelling nozzle on a turbojet engine incorporating means for augmenting propulsive thrust by the burning of addi tional fuel between the turbine and the propelling noZ- zle, hereafter referred to as afterburning An object of this invention is to provide for a propelling nozzle a control which is responsive to combustion in the afterburner.

A further object is to provide a control which will increase the prc-pellinU nozzle area as the afterburning starts, thereby preventing an initial loss of thrust and an excessive build-up of temperature at the turbine of the jet engine.

Another object is to provide a control which will not increase the propelling nozzle area if the afterburner fails to ignite, thus preventing the loss in thrust when augmentation is selected.

Another object is to provide a control which will automatically reduce the propelling nozzle area when the afterburning ceases.

A further object is to provide a control which will continue to maintain the increased nozzle area as long as the afterburner is in operation.

Another object is to provide a control incorporating manual over-ride means to increase the propelling nozzle area.

A further object of this invention is to provide a control responsive to the ratio of two absolute pressures.

Another object of this invention is to provide a device which will measure the ratio between two absolute pressures.

Further objects and advantages will be apparent from the following specification and drawings.

Fig. l is a schematic view of a turbojet engine including an afterburner showing the exhaust nozzle actuator control.

Pig. 2 is an enlarged schematic view of the exhaust nozzle actuator control.

Fig. 3 is a view showing the relationship of the ratio between turbine discharge gas pressure (P6) and compressor inlet pressure (P2) versus engine R. P. M. for various conditions.

Fig. 4 is an enlarged schematic view showing the actuating mechanism of the control.

Fig. 5 is a chart showing the relation of the pressure in passage 208 on either side of the null position of the actuating mechanism of the control.

Fig. 6 is an enlarged schematic view of a modication of the exhaust nozzle actuator control.

Fig. 7 is a schematic view of the actuating mechanism of the control modified to measure the ratio to which it is sensitive.

With reference to Fig. l, the turbojet engine 2 has a compressor 4, which, in the arrangement shown, is a centrifugal type, driven by a turbine 6. Combustion chambers 8 therebetween deliver air from the compressor to the turbine. An afterburner 10 is attached at the turbine outlet to provide a means of increaslng the thrust.

The engine 2 has two axially-spaced annular intake openings 12 to direct the incoming air into the two oppositely facing annular compressor inlets. Compressed air discharging from the compressor 4 passes to the turbine through the combustion chambers 8 where it is mixed with fuel from fuel nozzles 14. These fuel nozzles 14 receive fuel from the governor 15 through conduit 28. The fuel-air mixture is initially ignited within the combustion chambers 8 by a spark igniter 16. The governor 15 maintains the rotative speed of the turbine rotor assembly in accordance with the value selected by the power lever 17 by controlling fuel ow supplied through conduit and nozzles 14 to the combustion chambers 8.

From the turbine, the gases pass around a cone 18 into the diffuser section 19 of the afterburner. When the afterburner is operating, fuel is discharged into these gases from a plurality of fuel nozzles 26 located in the diffuser 19. Since the gases leaving the turbine 6 contain considerable unburned oxygen, the additional fuel introduced by fuel nozzles 26 provides a combustible mixture which may be initially ignited within combustion chamber 27 by ignition means 28 hereinafter described, which may be the type shown and claimed in the co-pending applications Serial No. 196,402 led November 18, 1950, and Serial No. 196,426 tiled November 18, 1959. The burning of this combustible mixture is stabilized in the combustion chamber 27 of the afterburner by ameholders 30 and 32. The burned gases discharge from the engine through the nozzle 44 whose area can be varied.

The variable nozzle 44 operates between a minimum opening for engine operation without afterburning and a maximum opening for operation of the engine with afterburning. A nozzle and actuating system, similar to the one shown with this invention, is shown and claimed in co-pending application Serial No. 193,734 tiled November 2, 1950. The actuating system consists of the cylinder 136, piston 132, connecting control rod 134, nozzle control rod 78, piston rod 138, a car 140, and a track mechanism 142 for said car.

The afterburner control system can be divided into three main parts. They are the following: (l) The fuel system, (2) the ignition means and (3) the exhaust nozzle actuator control. These three parts are closely coordinated by uid conduit connections and an electrical system.

The fuel system includes the fuel tank 46, the fuel booster pump 48, the fuel pump 50, the fuel meter 52 and the fuel nozzles 26. The fuel booster pump 48 is mounted on the fuel tank 46 and is connected to the fuel pump 50 by conduits 54 and 56. The fuel pump 50 is of the turbine type having a turbine rotor 58 mounted therein with an intake passage 6i) and exhaust passages 62 for the working uid. The working uid,

which is shown as compressed air supplied from the compressor outlet of the engine, is delivered to the intake passage by conduits 230, 64 and 66. A motor operated valve 63 is located at the junction of conduits 64 and 66 to control the operation of the fuel pump by controlling the ow of compressed air to the pump. The turbine rotor 58 drives an impeller 70 which provides the pumping action. The fuel pump 50 delivers fuel to the fuel meter 52 through conduit 72. The fuel meter 52 meters the fuel therein and injects it into the engine through conduit 74 and nozzles 26. The fuel meter represented herein may be any one of many types some of which are shown and claimed in co-pending applications Serial No. 196,423 led November 18, 1950 and Serial No. 196,414 led November 18, 1950.

The exhaust nozzle actuator control 76 connects pressures to the exhaust nozzle actuating cylinders by 3 a pressure relay valve 168 either to open or to close the exhaust nozzle as required. This lrelay valve 168 has three lands, 170, 172 and 174 which guide the valve in itsv cylinder bore 176. The cylinder bore 176 has six passages connected thereto, they are from left to right'in Fig. 2, a vent 178 to low pressure supply which may be compressor inlet pressure, a conduit 266 connected at its other end to the end of the cylinder 138 away from the nozzle, a conduit 230 which is connected at its other end to a high pressure supply shown as compressor discharge pressure, a conduit 262 which is connected at its other end to the end of the cylinders 130 nearest the nozzle, a Vent 18@ to low pressure supply, and a conduit 182 which serves as a drain. A spring 184 biases relay valve 168 to the right against one side of a piston cap 186. Piston cap 186 forms a chamber 19t) with a bore 191.

A pilot valve 188 connects chamber 190 either with a line 192 which supplies a source of iluid pressure or with a chamber 194 which is connected via conduit 25@ and 252 to a low reference pressure. To prevent the nozzle 44 from opening in a non-afterburning range (see Fig. 3) the source of uid pressure for line 192 is from a point in the afterburner fuel system downstream of the afterburner fuel pump. The pilot valve 188 has three lands, 196, 198 and 288, and moves axially in a cylinder bore 262. This cylinder bore has four passages connected thereto, starting from the top in Fig. 2 they are, a passage 294 which is connected at its other end to chamber 194, a passage 295 which is connected at its other end to a chamber 286 which is in turn connected to passage 192, a passage 268 which is connected at, its other end to chamber 190, and a passage 210 which is connected at its other end to chamber 194.

Pilot valve 188 is connected at its lower end to one end of a walking beam 212 located in chamber 194. This walking beam 212 is connected near each end between two bellows. Each set of bellows is attached by a slotted member 213 through which the walking beam 212 passes. A pin 215 pivotally attaches the walking beam at each end to member 213 of each set of bellows. The lower bellows at each end, 214 and 216, are evacuated.

Pressures at two different stations along the flow path of the gases through the power plant are used by the control 76 to sense combustion within the afterburner and to regulate the propelling nozzle accordingly. As shown in Fig. 1, these stations are the compressor inlet pressure which is connected by conduit 222 to bellows 218, located above bellows 214, and the turbine discharge pressure which is connected by conduit 79 to bellows 220, located above bellows 216. Other stations, such as those described and claimed in co-pending application Serial No. 196,425 led November 18, 1950, may be used.

A movable fulcrum 224 supports the walking beam 212 within a slot 226. A fulcrum shift piston 22S is located in bore 234) in control 76 above chamber 194. An arm 232 is connected at one end to the fulcrum shift piston 228 and at its other end to the fulcrum 224. The arm 232 passes through a slot 234 which connects bore 230 and chamber 194. The piston 228 can ltravel between two adjustment screws, a nozzle closing adjustment screw 236 and a nozzle opening adjustment screw 238. The nozzle opening adjustment screw 238 sets the value of the ratio of the pressures at the two different stations, represented by line X in Fig. 3, which value the ratio has to exceed to open the nozzle 44 when the two pressure stations shown in Fig. l are used. The nozzle closing adjustment screw 236 sets the value of the ratio of the pressures at the two different stations represented by line Y in Fig. 3, which value the ratio has to drop below to close the nozzle 44 when the two pressure stations shown in Fig. 1 are used.

A spring 248 biases piston 228 to the right against the nozzle opening adjustment screw 238. The charnlfer 242 formed by the bore 230 and the left end of the piston 228 is connected to chamber 194 by passage 244. The chamber 246 formed by the bore 230 and the right end of the piston 228 is connected to passage 288 by passage 248.

A manually operated control is provided to actuate the ay valve 16S in the event the automatic functioning of nozzle control 76 fails. This manual control consists of a bell lever 254 pivoted at 256, a link 258 and an actuating rod 260. Limit stops 264 and 268 are provided.

The igniter control 28 injects an amount of fuel in addition to that normally supplied into a combustion chamber 8 where it is ignited resulting in flame proparhrough the turbine into the afterburner for igniting a combustible mixture in the afterburner. Fuelis provided to the igniter control 28 from the main fuel system by conduit 80 which has a solenoid actuated shutoif valve S2 connected therein. The igniter control is connected by conduit S4 to conduit 74 which provides the actuating pressure to inject the additional fuel to provide ignition in the afterburner.

The electrical system may include a temperature control amplifrer 86 which during afterburner operation is sent a signal by therrnocouples 88 which sense turbine discharge temperature. Thermocouples 90 also sense turbine temperature but send their signal to a temperature gage 92. This amplifier when energized sends a signal to the fuel meter 52 4to attenuate fuel flow in accordance with some engine performance variable such as turbine discharge temperature and may also control the operation of a normally closed solenoid operated shut-off valve in the fuel meter 52. In the event excessive temperatures are reached at the turbine discharge the switch 93 will operate to permit the shut-off valve in the fuel meter to close. The afterburner switch 94 controls the amplifier 86, sets the motor operated valve 63, controls the fuel booster pump 48, and controls the opening of normally closed solenoid actuated shut-olf valve 82. While the attenuation of fuel ow has been described as being done by automatic means, it may be done manually if desired, watching gage 92 to regulate the temperature.

Since the actuating mechanism of this control 76 is responsive to the ratio of two absolute pressures it is shown that the pilot valve 188 of the control is moved relative to a null position, to be defined later, independently of either pressure. With reference to Fig. 4, the bellows 218 and 214 are equal in effective larea (A1=A11) and the bellows 220 and 216 are equal in etfective area (212:1422) to eliminate any unbalance from the pressure in chamber 194. As the pilot valve is hydraulically balanced, its motion is controlled by the balance of forces applied to the walking beam 212 by the `four bellows, 214, 216, 218, and 224). Land 198 on the piiot valve 188 cooperates with the end of passage 268 in bore 282 to provide either low pressure or a high pressure in conduit 288 whenever the pilot valve is infinitesimally moved in one direction or another from what may be defined as a null position of the pilot valve. he output of the actuating mechanism of the control is, therefore, a high pressure or a low pressurein conduit 2418 depending respectively upon whether the ratio of the pressure in bellows 218 to the pressure in bellows 229 is less than or more than the value established by the position of fulcrum 224.

Considering the balance of forces when the pilot valve 188 is at its null position, if P1 and P2 represent the absolute pressures at two appropriate stations in the gas dow through the engine, and a represents the distance between the point of application s of bellows 214 and 21S to the walking beam and fulcrum 224 and b represents the distance between the point of application t of bellows 216 and 220 to the walking beam and fulcrum 224, taking moments about the fulcrum 224 we may write:

where F1 and F2 represent mechanical spring forces contributed by the bellows, taken as positive forces when opposing the absolute pressures P1 and Pz.

Equation l may be rewritten:

From this equation it is apparent that a denition of the force balance existing when the pilot valve is at "null, in terms of the pressure ratio Pi/Pa, is independent of the pressure P; but is independent of the pressure P2 only when F1/Fz=b/a. in certain cases it may be desired to use the bellows spring forces F1 and F2 to obtain a variation in the ratio Pi/P2 at null as a function of P2. ln the general case, however, where the pressure ratio setting is desired independent of both pressure P1 and pressure P2 it is required that F1/Fz=b/a to establish this independence. if F1 and F2 are established to make Fi/Fz=bv/a at one particular value of b/n, it is obvious that F1/F2 will not equal b/a at some other value of b/a. It is apparent, therefore, that the null point pressure ratio setting can be made independent of P1 and P2 for all values of b/ a only by making lt is apparent that as fulcrum 224 is moved to change the pressure ratio setting, the mechanical forces F1 and F2 contributed by the bellows must remain zero. This requires that the locus of fulcrum 224` relative to the walking beam be such that with the pilot Valve 188 at null position no motion of points s or t results when the fulcrum 224 is moved; otherwise the mechanical resilience of the bellows would reestablish finite values of F1 and F2. In the arrangement disclosed these requirements are met by making the slot 226 in the walking beam parallel to the center line s-t and by moving fulcrum 224 in a line parallel to, and displaced to locate, center line s-t such that the pilot valve remains at its null position when the bellows forces P1 and F2 equal zero.

From Figure 5 it is further apparent that when the pressure ratio P2/P1 is in excess of (P2/P1)null the unbalance then resultant in the forces acting on the walking beam cause the walking beam to rotate in a clockwise direction about the fulcrum 224 and displace the pilot valve to move away from its null position in the direction such that pressure from conduit 205 is supplied to the output passage 208. In a like manner when the pressure ratio Pz/Pi is less than (P2/P1)null as defined by Equation 3, the pilot valve is displaced to provide the low reference pressure of chamber 194 in passage 208.

With reference to Fig. 6, this modified control connects pressures to the exhaust nozzle actuating cylinders 130 either to open or to close the nozzle as required in the same manner as the control in Fig. 2. A pilot valve 272 connects chamber 190 either with line 192 which supplies a source of uid pressure or with conduit 274 which is connected to drain. The pilot valve 272 is also constructed in the same manner as the pilot valve in Fig. 2. However, the cylinder bore 202 in which the pilot valve 272 moves axially has a dierent arrangement of passages connected thereto, starting from the top in Fig. 6 there are, a passage 204 which is connected at its other end to chamber 194, a passage 205 which is connected at its other end to a chamber 206 which is in turn connected to passage 192, passage 208 which is connected at its other end to chamber 190, and a passage 276 which is connected at its other end to conduit 274.

Pilot valve 272 is connected at its lower end to one end of a walking beam 2l2 located in chamber 194. Walking beam 212 is attached diierently from the walking beam in Fig. 2 as it is connected near each end by only one bellows. Each bellows is attached by a bifurcated member 278 through which the walking beam passes and is pivotally attached by a pin 215.

ln this view there are also shown restraining means for walking beam 212. Bearing faces 602 and 604 are formed on each end of said walking beam and engage anti-friction bearings 605 and 608, respectively, to prevent translation yet allow rotative movement of said walking beam. These bearings, 666 and 603, are mounted on pins 6l@ with the housing. While these means are only shown in this view they are equally applicable in Figs. 2, 4 and 7.

As mentioned before in relation to Fig. 2, pressures at dierent stations along the ow path of the gases through the power plant are used by the control to sense combustion within the afterburner and to regulate the propelling nozzle accordingly. The stations shown are the compressor inlet pressure which is connected by conduit 222 to bellows 21S, and the turbine discharge pressure which is connected by conduit 79 to chamber 194. Bellows 270 is evacuated.

The fulcrum shift piston and associated mechanism for moving and controlling movable fulcrum 224 is the same as shown in Fig. 2. However, in this modification the chamber 242 is connected to passage 276 by passage 277 instead of being connected to chamber 194 as in Fig. 2, Chamber 194 is also closed olf from passage 252 and 250. This moditied control operates in the same manner as the control shown in Fig, 2.

With reference to Fig. 7, this measuring device is a modification of the actuating mechanism of the control as shown in Figs. 2 and 6. While shown with a four bellows arrangement as shown in Fig. 4, a two bellows arrangement as shown in Fig. 6 may be used. This modification consists essentially of changing the porting of pilot valve 138g so that an increase in the ratio of absolute pressures, Pz/Pi, results in a low pressure in passage 300, and a decrease in the ratio results in an increase of pressure in passage 300. This is done by having passage 205, the passage carrying high pressure, enter bore 202 below passage 300 and having passage Sli), the passage carrying low pressure, enter bore 202 above passage 300. Passage 300 is now connected only to the chamber 245 at the right end of the fulcrum shift piston 228.

Equation 3 may be transposed P1 null-b A-2 For a particular bellows area ratio Ai/Az, the product ei/ b (Ai/A2) is determined by the position of fulcrum 224. So, for every position of fulcrum 224 there exists a pressure ratio which obtains at the null position of the pilot valve 18851.

When the ratio P2/P1, of the applied absolute pressures is less than the ratio required to bring the pilot valve 188g to its null position at the value of n/b resulting from a given position of fulcrum 224, the pilot valve 188g will be displaced upwards to port high pressure from passage 205 through passage 300 to urge the fulcrum shift piston 228 to the left against spring 240, consequently decreasing the ratio of a/b. As the piston moves the fulcrum tothe left, the ratio of a/b approaches thevalue corresponding to the null.position of therpilotvalve 188a at'theapplied pressure ratio, and thek piston comes to rest when the nullposition is reached. ln a like manner, an increase. in the pressure ratio.causes thefulcrum bar`224 to kmove to the right until. the pilot valvel138a is again returned to its null position.

Thus, for any pressure ratio, the fulcrum shift piston 228 will.y move to position the fulcrum 224 in accordance with said ratio. Accordingly, some mechanism may be attached to the piston for a control or for measurement. In Fig. 7 .an indicating device is shown. A rack 302 is lpositioned'by a rod 304attached to said piston. This rack :drives gear 306 which will attain some angular position according to the pressure ratio. This gear 306 is connected'by a rod 308 to an indicating hand 310 which indicates pressure ratio directly on a calibrated scale 312.

While in the following operational disclosure the control 78 is described .as being connected to compressor inlet pressure (Pz in Fig. 2 and Fig. 6) and turbine discharge pressure (P6 in Fig. 2 and Fig. 6) the actuating mechanism of the control operates similarly for any two pressures chosen. However, the shape and rela tive positions of curves A, .B and C in Fig. 3 will vary depending upon what stations are used for the ratio Pz/Pi.

Operation Afterburner operation is initiated by placing switch 94 in its on position. This movement turns the temperature control amplifier on which in turn opens a normally closed solenoid operated shut-off valve in the fuel meter and sends a signal to the afterburner fuel meter for attenuating fuel flow therethrough. This movement ofthe switch also places motor operated valve 68 in open position, starts the fuel booster pump 48 and opens normally closed solenoid actuated shut-off valve 82.

The operation of the fuel booster pump forces fuel from the fuel tank 46 through conduits 54 and 56 tothe impeller 70 of the fuel pump 50. The opening of the motor operated valve 68 allows compressed air to be directed from the outlet of the engine compressor 4 through conduits 230, 64 and 66 against turbine 58 to drive the impeller 70.

The impeller 70 then delivers fuel to the afterburner fuel meter 52. This fuel meter 52 meters fuel as a function of compressor pressure rise and under the inuence of the temperature control amplifier and this fuel passes by a vnormally closed solenoid shut-olf valve, which is now open, through conduit 74 to the fuel nozzles 26.

The opening of the normally closed solenoid actuated shut-Dif valve 82 permits a source of fuel to be supplied to the igniter 28 through conduit 80. The pressure of the fuel in conduit 74 is transferred to the igniter by conduit 84 which pressure permits kfuel which has passed normally closed solenoid actuated valve 82 to be injected from the igniter into a-combustion chamber 8. Ignition of the injected fuel results in ame propagation through the turbine to the tail pipe resulting in ignition in the afterburner of the fuel being nozzles 26.

As the afterburner` ignites, the exhaust nozzle actuator control 76 has its moving parts approximately in the positions shown-in Fig. 2 (these positions also hold for the control shown in Fig. 6); compressor inlet pressure admitted'to bellows 218 through conduit 222 and turbine discharge pressure admitted to bellows 220 through conduit 79 positioning pilot valve 188 so that land 198 opens entranceto 208 to 210 and closes off the entrance to conduit 208 from conduit 205, spring 184 biasing relay valve 168 to the right thereby directing compressed air from conduit 230 to conduit 266 and connecting conduit 180 to conduit..262 to maintain nozzle 44 in its closed position, and .spring 240 biasing fulcrum shift piston to the right against the nozzle opening adjustment screw introduced through 238 thereby positioning the movable fulcrum 224 to the right. At this point in the sequence of operation with the .engine operating .innthe afterburner operating range the ratio of Pes/P2 is found on curveB (see Fig. 3), the curve marked afterburner olf with nozzle closed. .With fulcrum 224 in its right-hand position this ratio is less than that required, line X, to move the pilot valve from the last described position and the nozzle remains closed. It is necessary, in order for the nozzle to be opened, to obtain a ratio of Ps/Pz.above a'value represented by line X, a vaiue which is determined by the position of the nozzle opening adjustment screw V238.

The ignition of fuel within the afterburner results in an increase in turbine exhaust gas pressure above that normally obtained without afterburning. With ,the engine operating in the afterburner operating range the start of the afterburning raisesv the value of Pe so that the ratio of Pta/P2 is found on curve'A' (seevFig.4 3), which in this range is above line X. This increase in turbine exhaust gas pressure is transmitted to bellows 220thereby increasing the pressure in this bellows causing its end ofthe vwalking beam 212 to move down, thereby moving, pilot valve 188 down and connecting passage 208 to passage 204 admitting the actuating uid from conduit 192 to pass into chamber 190 and move relay valve 168 to the leftagainst spring 184 and connect conduit 230 kto conduit 262 to direct compressed air to the side of the cylinders which will cause the nozzle 44 to open and also connectconduit 266 to conduit.178. As the actuating iluid .in passage 208 passes to chamber 190, it is directed by passage 248 into chamber 246 and moves the fulcrum shift piston 228 .to the left against the nozzle closing adjustment screw 236 so that the pressure resulting from the opening of the exhaust nozzle 44 will now be suflicient to maintain the pilot valve 188 in its down position. When the nozzle opens, the ratio of Pri/P2 moves downto curve B (see Fig. 3) marked afterburner on with nozzle open and with fulcrum 224 in its left position this ratio is now enough to maintain the nozzle in its open position. The pressure in this conduit 262 is transmitted by conduit 98 to a normally closed pressure switch 96 in the electrical line to the normally closed solenoid actuated shut-off valve 82 which opens said switch thereby. closing the shut-off valve 82 -preventing a iiowof fuel tothe igniter To intentionally cease operation of the afterburner the afterburner switch 94 is turned to its off position. This turns the temperature control amplifier 86 oif thereby turning oif a supply of current to a normally closed solenoid operated shut-off rvalve in the. fuel meter and the normally closed solenoid actuated shut-off valve 82 in conduit 80. The movement of the switch to the off position also closes the motor operated valve`68 and turns off the afterburner fuel booster pump 48. 1t will be seen that with the fuel pump 50 and fuel booster pump 48 off line 192 loses its pressure therebyV permitting spring 184 to move relay valve 168 to the right and connect conduit 230 to conduit 266 to direct compressed air to the side of the cylinders which will cause the nozzle to close and also connect conduit 262 to conduit 180. While the afterburner has been described as intentionally turned oif, the following disclosure holds for the operation when the combustion in the afterburner ceases unintentionally leaving the afterburner fuel system on. At this point inthe sequence of operation with the engine still in the afterburner operating range the ratio of Pes/P2 is found on curve C (see Fig. 3) marked afterburner off and nozzle open. With fulcrum 224 in its left position this ratio is not enough to maintain the nozzle in'its open position since the ratio is at a value below the value Arepresented -by line Y, a value which is determined by the position of the nozzle closing adjustment screw 236. This vdecrease in afterburner pressure is transmitted to bellows 220 thereby decreasing the pressure in this bellows causing'ts end ofthe walking beam 212 to move up, thereby moving pilot valve 188 up so that land 198 closes orf the entrance to passage 208 from passage 25. This movement also connects passage 208 to passage 210 so that the iuid in chambers 190 and 246 will be connected to chamber 94 permitting this fluid to be forced into the uid in chamber 194 by the spring force applied on each end of relay valve 16S and fulcrum piston 228. This action permits both the relay valve 168 and fulcrum piston 228 to move to the right. This places the control 7 6 in the position it was in before afterburning was initiated, with relay valve 168 being biased to the right directing compressed air from conduit 230 to conduit 266 to close nozzle 44 and maintain its closed and connecting conduit 262 to conduit 118i). Now with the nozzle closed the ratio Pta/P2 moves up to curve B (see Fig. 3) marked afterburner off with nozzle closed. With fulcrum 224 in its right position this ratio is now enough to maintain the nozzle in its closed position. This reduction of pressure in conduit 252 is conveyed to normally closed pressure switch 96 by conduit 98 thereby permitting the switch to be closed to permit current to pass to valve 82 upon the next starting of the afterburner.

Although a specic exhaust nozzle actuator control has been shown and described herein for purpose of illustration, it will be evident of those skilled in the art that the invention is capable of various modifications and adaptations within the scope of the appended claims.

i claim:

l. In combination: a turbo-jet engine having a variable area propelling nozzle through which gas from the engine is discharged; means for adjusting the area of said nozzle, valve means to control said adjusting means; a pivoted lever, bellows means for applying forces to said lever proportional to two absolute pressures existing at two spaced points in the gas iiow path of the engine; and second valve means actuated by said lever to control said iirst valve means as a function of a predetermined ratio between said absolute pressures; piston means operatively connected to said pivoted lever to vary the value of said predetermined absolute pressure ratio; and said piston means actuated by said second valve means.

2. In combination: a turbo-jet engine having a variable area propelling nozzle through which gas from the engine is discharged; means for adjusting the area of said nozzle, valve means to control said adjusting means; a pivoted lever, bellows means for applying forces to said lever proportional to two absolute pressures existing at two spaced points in the gas ow path of the engine; and second valve means actuated by said lever to control said rst valve means as a function of a predetermined ratio between said absolute pressures; piston means operatively connected to said pivoted lever to vary the value of said predetermined absolute pressure ratio; and said piston means actuated by said second valve means; and manual means for actuating said first valve means.

3. In combination: a turbo-jet engine having an afterburner, and a variable area propelling nozzle through which gas from the engine is discharged; means for adjusting the area of said nozzle, valve means to control said adjusting means; and second valve means responsive to the ratio ot' absolute pressures existing at two spaced points in the gas flow path of the engine for actuating said first valve means, a conduit supplying fuel to said afterburner; and said rst valve means responsive to fuel pressure in said conduit.

4. In combination: a turbo-jet engine having an afterburner, and a variable area propelling nozzle through which gas from the engine is discharged; means for adjusting the area of said nozzle, valve means to control said adjusting means; and second valve means responsive to the ratio of absolute pressures existing at two spaced points in the gas ow path of the engine for actuating said first valve means, a conduit supplying fuel to said afterburner; and said first valve means responsive to lf3 fuel pressure in said conduit; and manual means for actuating said first valve means.

5. In combination: a turbo-jet engine including a compressor, a turbine driving said compressor, a combustion chamber therebetween, an afterburner, and a variable area propelling nozzle through which gas from the engine is discharged; means for adjusting the area of said nozzle; and a control means responsive to a rst ratio of absolute pressures existing at two spaced points in the gas ow path of the engine for actuating said adjusting means in a manner to increase the propelling nozzle area and responsive to a second ratio of absolute pressures existing at said two spaced points in the gas How path of the engine for actuating said adjusting means in a manner to decrease the propelling nozzle area, a conduit supplying fuel to said afterburner; and said control means also responsive to fuel pressure in said conduit to decrease the propelling nozzle area when said fuel pressure falls below a predetermined value.

6. In combination: a turbo-jet engine including a compressor, a turbine driving said compressor, a combustion chamber therebetween, an afterburner, and a variable area propelling nozzle through which gas from the er1- gine is discharged; means for adjusting the area of said nozzle; and a control means responsive to a first ratio of absolute pressures existing at two spaced points in the gas ow path of the engine for actuating said adjusting means in a manner to increase the propelling nozzle area and responsive to a second ratio of absolute pressures existing at said two spaced points in the gas ow path of the engine for actuating said adjusting means in a manner to decrease the propelling nozzle area, a conduit supplying fuel to said afterburner; and said control means also responsive to fuel pressure in said conduit to decrease the propelling nozzle area when said fuel pressure falls below a predetermined value; and manual means to increase the propelling nozzle area.

7. An aircraft jet propulsion system comprising in combination, a jet propelling nozzle, means movable to adjust the area of said nozzle, a piston to move said means, and a nozzle control, said control having a relay valve for directing a working uid to one side of said piston or the other, a pilot valve for moving said relay valve in one direction, a spring for moving said relay valve in the other direction, a chamber, a walking beam in said chamber, a fulcrum for said walking beam, said walking beam being attached to said pilot valve for moving it, two pairs of oppositely mounted beilows in said chamber, said walking beam being connected at one end to one pair of the bellows and at its other end to the other pair of bellows, and a conduit connecting one bellows to an engine operating pressure.

8. An aircraft jet propulsion system comprising in combination, a jet propelling nozzle, means movable to adjust the area of said nozzle, a piston to move said means, and a nozzle control, said control having a relay valve for directing a working Huid to one side of said piston or the other, a pilot valve for moving said relay valve in one direction, a spring for moving said relay valve in the other direction and a walking beam attached to said pilot valve for moving it, said walking beam being responsive to a pressure on each end and having a movable fulcrum, said fulcrurn being mounted on an arm xed to a shift piston.

9. An aircraft jet propulsion system comprising in combination, a jet propelling nozzle, means movable to adjust the area of said nozzle, a piston to move said means, and a nozzle control, said control having a relay valve for directing a working uid to one side of said piston or the other, a pilot valve for moving said relay valve in one direction, a spring for moving said relay valve in the other direction and a walking beam attached to said pilot valve for moving it, said walking beam being responsive to a pressure on each end and having a movable fulcrum, said fulcrum being mounted on an 1 1 arm fixed to ashaftpiston, said pilot valve `being operable to move said shift piston. y

.1 0. Angailraftnjet :propulsion system1comprising in combination, a -jet propelling; nozzle, lmeans movable to adjust lthe area of said nozzle, apistonto moveV said means, and agnozzlecontrol, said control having a .relayvalve-tor directingaworking uid to -oneside .of said piston ,for the other, apilot valve. for.;.directingg;pressures ttosmove` saidv relaynnfrlve, and awalkingbeam, attachedfto; saidpilot valve for; movingV it, said Walking -beam being. responsive .to .a pressure ron earchndrandhavingta-movable fulcrum, said fulcrurnY being mounted on an arm fixed toa shiftpiston, said pilot valve being .operable to ymove said shift piston, and ;n;,teans. adjustable tolimit the ,travel of .the shift piston. 11. A turbo-,jet enginegincluding a compressor, a turbine driving-said'compressor,La combustion chamber receiving compressed-air `from the compressor and discharging it to @the turbine, an fafterburner.- and an exhaust nozzle throughv-whichggasfrom the 1atterburner is discharged, means including a -piston for adjusting said nozzle, and nozzle-control `for operating said piston having a housing, arelayvalve slidable in a bore in said housing, a conduit 'connecting said bore to aworking uid, a second conduit connecting said bore ,to one side of said piston,

a'third conduit connecting said bore -to -the other side of said piston, said Vrelay valve being constructed so. that in one position it will admit theworking uid from the rst conduit pto Athe second conduit and in anotherposition it--Willadmt the working uid vfrom the'irst conduit to the third conduit, a spring biasing said relay valve into one position, a pilot valve slidable ina second bore in said housing, a fourth conduit connecting `one end of said relay valve to said second bore, a -fth conduit connecting said second Abore to a Working uid, said pilot valve being constructed so that in one positionit will admit the working iluid yfrom the fifth conduit to the fourth conduit where it acts against--theend of said relay valve to move the relay valve into its other positionand in another position ibwill block oft the fifth conduit from the fourth conduit, a chamber in saidhousing, ber connected to bellows, said beam being attached to said pilot valve to move it, and a conduit connecting a bellows to said afterburner to conduct turbine discharge pressure to said bellows.

l2. In combination: aturbo-jet engine having a variable area propelling nozzle through. which gas from thelenginc is discharged; means for adjusting the area of said nozzle, valve means to control said adjusting means; ,a control lever; pressure responsive means rfor supplying forces to said lever proportional to. two pressuresvv existing at two a walking beam in said chaml 2 spaced points in the gas flow path of the engine; and fourth means actuated by saidl lever t0 control; 'said rst valve means as a function of a predetermined .ratio between Ysaid pressures; ifth means .operatively connected to said lever to ,vary the value of the predetermined` pressure ratio; said -fth .means being actuated by said .fourth means.

13. In combination: a turbo-jet engine. having avariable area propelling nozzle through which gas.- from the engine is discharged; means lforadjusting thearea Vofsaid n0zz1e,.valve means to control said adjusting. meansga control lever; pressure responsive means for supplying forces to said lever4 proportional to two pressures existing at two spaced points in the gas ow path ofthe engine; and second valve means actuated by said lever .tocontrol said first valve means as a function of apredetermined ratio between said pressures; fth means operatively connected to said lever to vary the value `of the predetermined pressure ratio; said. iifth means being actuated. by said second valve means. Y

14. In combination: a turbo-jet engine havingayariable area propelling nozzle through which-gas fromtthe engine is discharged; means for adjusting 'the area .of said nozzle, valve means to control said adjusting-means; a control lever; pressure responsive means for Supplying forces to said lever proportional `to two pressures existing at two spaced points in the gas flow path of the engine; and fourth means actuated by said lever to control said rst valve means as a function of a predetermined ratio between said pressures, piston meansV operatively connected to said lever to vary the value of the predetermined pressure ratio; saidv piston means being actuated bysaid fourth means.

.References Cited in the tile of this patent UNITED .STATES PATENTS Price Sept. .29, 

